It is common in industrial hydraulic fracturing activities to utilize water or aqueous mixtures in the extraction of product. Such fluids are used in various fluid pathways of a hydraulic fracturing system, which include conduits of wellheads and various production tubulars and of deposit or reservoir wellbores, including distant cracks and fractures in the rock of the deposit or reservoir. A common problem encountered is the formation of scale on the inside surfaces of such conduits. Water or aqueous mixtures can contain a variety of alkaline earth metal cations, such as calcium, barium and strontium as well as a variety of anions such as bicarbonate, carbonate, sulfate, phosphate and silicate. When such ions are present in sufficient concentrations, they can combine to form precipitates. Scale, formed by the deposition of any of several types of such precipitates can coat surfaces in contact with the water or aqueous mixtures. Buildup of such scale on inside surfaces of conduits can, among other things, obstruct fluid flow. Common scales include Calcite, Barite, Celestite, Anhydrite, Gypsum, Iron sulfide, Halite and various “Exotic” scales, such as calcium fluorite, zinc sulfide, and lead sulfide sometimes found with high temperature/high pressure (HT/HP) wells.
The petroleum industry technique known as hydraulic fracturing or, more informally, “hydrofracking” and “fracking,” is a widely used and effective method of enhancing the recovery of oil and natural gas from deposits or reservoirs once thought to be difficult or impossible to develop economically. Hydraulic fracturing has been employed in combination with both vertical and horizontal drilling.
Hydraulic fracturing involves injecting a mixture of water, sand or sand-sized particles, and chemical additives into a subsurface petroleum reservoir at high pressure. Injection pressures create small interconnected cracks in the rock and hold open small fractures, about as wide as one or two grains of sand, in the vicinity of the well. These fractures serve as fluid pathways in the reservoir, permitting the fluids in the reservoir to flow more readily to the wellbore.
Scale inhibitors are used in such production wells to prevent scaling in the formation and/or in the production lines downhole and at the surface. Scale build-up decreases permeability of the formation, reduces well productivity and shortens the lifetime of production equipment. In order to clean scales from wells and equipment it is necessary to stop the production which is both time-consuming and costly.
Current scale inhibitors and methods of using such scale inhibitors have the disadvantage of the difficulty in releasing the inhibitor into the well over a sustained period of time. As a result, treatments must repeatedly be undertaken to ensure that the requisite level of inhibitor is continuously present in the well. Such treatments result in lost production revenue due to down time.
Scale prevention is important to ensure continuous production from existing reserves. Scale inhibitors and treatment methods for oil and/or gas wells are therefore sought that provide scale inhibiting chemicals that may be released over a sustained period of time. It is desired that such methods not require continuous attention of operators over prolonged periods.
Extensive efforts have been invested into finding chemical additives and methods limiting the dissolution rate of the inhibiting chemicals to achieve the optimal economic recovery of oil or gas. Such efforts continue, indicating a clear need for scale inhibitors and methods of using such inhibitors that exhibit slower, sustained release in the high temperature environment of hydraulically fractured oil and gas wells.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR § 1.56(a) exists.